Many DGPS corrections networks exist, including FAA WAAS, OmniStar, JPL, USCG Beacons, local commercial networks, local community cooperatives networks, and local government funded networks. In the above examples, the deployment and maintenance of the reference station hardware is funded in one of the following ways: the government, commercially (paid for by subscriptions from users), commercially (deployed to encourage sales of receivers) or margins on roving units pay for reference network privately. The network owns and/or operates the reference stations.
In wide area networks (e.g., WAAS, OmniStar, and JPL), geosynchronous satellites provide differential correction information. The footprint of the beams from the geosynchronous satellites is large, resulting in a wide area network. A relative few, such as 10-30, reference stations are provided in any footprint of the geosynchronous satellites for hemisphere corrections. The reference stations send differential corrections on land lines to a central facility. Weather based model information for further improving location calculation may also be generated by the central facility. The central facility provides the differential corrections and any model information to the geosynchronous satellites for beaming to mobile devices. The mobile devices determine location with differential based accuracy from global positioning satellite (GPS) signals, the differential corrections and any model information. The closest reference station may be over 100 miles away from the mobile device. However, carrier phase based position determinations may provide about 5-12 inch level accuracy.
For local area systems (e.g., USCG Beacons), terrestrial based communications provide differential corrections. One or more local reference stations transmit differential corrections on a radio transmitter or modem. Receivers within the range of the radio transmitter or modem calculate position based on the differential corrections and signals received from the reference stations.